Application of hydrochemical and tracer techniques to investigate the source of seepage water in deep gold mines: a case study at South Deep Gold Mine, Gauteng Province, South Africa

Abstract

A hydrogeological study was conducted to investigate the possible sources of seepage at South Deep Gold Mine (SDGM), near Westonaria town, Gauteng Province. The aim of the study was to promote efficient mine water management through a better understanding of the source of seepage by utilising integrated hydrochemical and tracer techniques to assist the mine with strategic mine planning and design, and financial implications. Underground field observations, cross-sections, mine survey data, monitoring borehole data were used to provide a better understanding of the hydrogeological characteristics at SDGM. Hydrochemical facies characterised seepage water into 4groups: (i) Mg-SO4water type, suggesting SO42-contamination from the mine and/ or a mix of different water types; (ii) NaCl water type, indicatingregional groundwater source; (iii) Ca-SO4 water type due to the existence of sulphides bearing rocks and; (iv) Ca-Mg-SO4 water type signifying SO42-contaminated water as a result to historical and/ or current mining activities .The stable isotope analysis conceptually characterised the seepage water into three groups: (i) un-evaporated isotopic composition indicating condensation effect/water mass mixing, (ii) local rain composition suggesting recharge occurring through direct rainfall, and (iii) samples on the evaporation line suggesting secondary evaporation during and/ or before rainfall recharge. Seepage water contained detectable amounts of tritium indicating recharge/aquifer renewability. Tritium signature varied from 0.0 TU to 1.8 TU. Tritium content between 0.8-1.8 TU was interpreted as recharged in the past +20 to 35 years and the low tritium content (<0.8 TU) samples are categorised as sub modern, recharged before 1950s, indicating that the recharge mainly occurred approximately +35 to +70 years ago. Based on the hydrogeological conceptualisation of the main source of seepage within the study, seepage is mainly associated with or observed near backfilled areas, places closer to active mining, along the abutment zones, the geological structures such as faults and mining-induced fractures, worsened/compounded by inadequate mine-water management. Seepage water was also observed on drilled boreholes which holed to active or old mining levels. Possibly groundwater may flow into the mine void through borehole voids that drilled up to the lava position or intersected structures with the potential of connecting the aquifer and the mine void. This report recommends strict and long-term excess water and service water management underground to ensure the safety of the mine`s employees, minimizing corrosion on rock support, and damage of mine property. A better understanding of the source and cause of seepage at the mine will assist in safe mine planning and enhance management of service and excess water underground